How to use Light Selection Guide
Suggestions on how to select a headlight for your commuting situation:
1.
Verify latest sunrise/sunset date for your location.
North America: Dec 14, 2004 Sunrise 7:13am, Sunset 4:35pm
2.
Figure out how much time you need if no flats/delays
30 minute commute: 7:30-8:00am, 5:00-5:30 pm
AM, 0 minutes; PM 30 minutes; Day: 30 minutes
60 minute commute: 7:00-8:00am, 5:00-6:00 pm
AM, 13 minutes; PM 60 minutes; Day: 73 minutes
3.
Add 30 minutes for worst case, flat, equipment failure and weather delay
30 minute commute -- 60 minutes burn time
60 minute commute -- 103 minutes [ 1 hr, 23 min] burn time
Sort the light selection guide for your perfect light
4. Sample Sort -- Sort light chart: fastest speed, city lights
Sort #1, K, City Max Speed, decreasing
Sort #2, G, Run time, decreasing
Sort #3, C, Price, ascending
5. Sample Sort -- Sort light chart: cheapest, fastest
Sort #1, C, Price, ascending
Sort #2, K, City Max Speed, decreasing
Here is the skinny on twilight, unfortunately too many try to ride/drive during Civil or Nautical twilight without lights on and only turn on the lights at astronomological twilight. Simple summary:
4 Standard levels of darkness transitions:
Actual sunrise/sunset -- still can work without lights
Civil twilight -- see objects and some details
nautical twilight -- see object outlines
astronomical twilight -- night
Here's the official word:
http://aa.usno.navy.mil/faq/docs/RST_defs.html
Civil twilight is defined to begin in the morning, and to end in the evening when the center of the Sun is geometrically 6 degrees below the horizon. This is the limit at which twilight illumination is sufficient, under good weather conditions, for terrestrial objects to be clearly distinguished; at the beginning of morning civil twilight, or end of evening civil twilight, the horizon is clearly defined and the brightest stars are visible under good atmospheric conditions in the absence of moonlight or other illumination. In the morning before the beginning of civil twilight and in the evening after the end of civil twilight, artificial illumination is normally required to carry on ordinary outdoor activities. Complete darkness, however, ends sometime prior to the beginning of morning civil twilight and begins sometime after the end of evening civil twilight.
Nautical twilight is defined to begin in the morning, and to end in the evening, when the center of the sun is geometrically 12 degrees below the horizon. At the beginning or end of nautical twilight, under good atmospheric conditions and in the absence of other illumination, general outlines of ground objects may be distinguishable, but detailed outdoor operations are not possible, and the horizon is indistinct.
Astronomical twilight is defined to begin in the morning, and to end in the evening when the center of the Sun is geometrically 18 degrees below the horizon. Before the beginning of astronomical twilight in the morning and after the end of astronomical twilight in the evening the Sun does not contribute to sky illumination; for a considerable interval after the beginning of morning twilight and before the end of evening twilight, sky illumination is so faint that it is practically imperceptible.
So on darkest day for US, 12.14.2005 the times are
sunrise/sunset--------- 7:13 am, 4:35 pm
civil twilight----------- 6:42 am, 5:05 pm
nautical twilight ------- 6:08 am, 5:39 pm
astronomical twilight --- 5:36 am, 6:02 pm